Just recently Ultimate Marvel vs. Capcom 3's director Ryota Nitsuma has been speaking on Twitter about Capcom characters that were considered to join the update's roster. Most people already know Fou-Lu was one of the many characters mentioned before, but here Nitsuma elaborates a bit more about why he was dropped. More interesting is the fact Nina (which one he doesn't say) and Katt were at one point considered too!

He has good domestic popularity and has more than enough stuff to use (energy sword, monster servants, shapeshifting, dragon forms), but was rejected because that'd have been way too much work and he is not very popular overseas.

Nina of "Breath of Fire" was the candidate character, based off Nina from "Breath of Fire 1". I personally prefer Nina from 3. I really wanted to use something from every generation of Nina, making her similar to Mega Man from Smash Brothers. That was my aspiration.

This is incredible to hear, and hopefully a harbinger of things to come. Fou-Lou seems like he would be a longshot to me given his relative domestic obscurity, which is apparently what the development team ultimately decided, but he would be beastly for that kind of game, and if done right would probably generate enough interest that the series itself could get more steam from mainstream gamers, the same way that the Fire Emblem characters in Melee renewed interest in that series in the US.

I see no reason why Nina at least couldn't make it in. I mean, they have Strider, so there's clearly some regard for relatively obscure series with historical significance. And hopefully with Marvel Infinite these characters might have another chance.